Method for Electrodeposition of an Electrode on a Dielectric Substrate

ABSTRACT

A method for the electrodeposition of an electrode including a metallic electrode material ( 40 ) on a dielectric substrate ( 10 ), including the following steps: depositing an electrically conductive polymer layer ( 20 ); masking the electrically conductive polymer layer ( 20 ) using a mask; electrodepositing the metallic electrode material ( 40 ) on the electrically conductive polymer layer ( 20 ); removing the mask; and removing or deactivating the excess conductive polymer layer ( 20 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of co-pending U.S.Provisional Patent Application No. 61/413,493, filed on Nov. 15, 2010,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates generally to a method for the electrodeposition ofan electrode on a dielectric substrate.

BACKGROUND

Various methods for depositing metallic electrodes on a substrate areknown.

According to a first method, to prevent diffusion between an electrodemetal and the substrate, a barrier layer (e.g., Ni) and then theelectrode metal (e.g., Au) are plated onto a base metal, such as, forexample, Cu. The electrode is therefore comprised not merely of theelectrode metal. Since a barrier layer is not perfect, an alloy may formand the electrode metal may therefore become contaminated. In addition,corrosion problems can occur in the barrier layer if it containsinhomogeneities.

According to another method, the electrode metal (e.g., Au) isselectively deposited onto a metallic foil (e.g., a Cu foil), which isdisposed on a carrier. After the electrode metal has been deposited, thefoil is separated from the carrier and is laminated into a base materialusing the electrode-metal side. Next, the foil is removed in an etchingstep and only the electrode metal remains on the base material. Whenmetals are used that alloy easily with one another, such as, forexample, Cu and Au, these metals can inter-diffuse during deposition andthe subsequent processes. The impurities that are created as a resultcan cause problems when the electrode metal is used for electrodes thatare implanted in an animal or human body.

Furthermore, it is known to sputter a carrier foil with the electrodemetal, to apply and pattern a photoresist, and to plate the electrodemetal thereon via electrodeposition. The photoresist is removed and agentle etching step is used to etch away the layer that was applied bysputtering. To ensure good adhesion of the electrode metal on thesubstrate, another metal layer such as, for example, Cr is usuallyrequired to promote adhesion. In addition to the process steps beingelaborate and numerous, such an adhesion-promoting layer can negativelyinfluence the biocompatibility of the electrode metal.

The problem addressed by the invention is that of creating a method fordepositing an electrode on a dielectric substrate, in the case of whichthe diffusion of foreign material into the electrode is at leastreduced.

SUMMARY

The problem is solved according to the invention by the features of theindependent claim(s). Favorable embodiments and advantages of theinvention result from the further dependent claims and the description.

A method for the electrodeposition of an electrode including a metallicelectrode material on a non-conductive dielectric substrate is provided,comprising the following steps:

-   -   Depositing an electrically conductive polymer layer on the        substrate;    -   Masking the electrically conductive polymer layer using a mask;    -   Electrodepositing of the metallic electrode material on the        electrically conductive polymer layer;    -   Removing the mask; and    -   Removing or deactivating the excess conductive polymer layer.

The excess conductive polymer layer can be deactivated (i.e., minimizethe conductivity), e.g., by reduction or oxidation of the conductivepolymer. As an alternative, the conductive polymer can also be removed,e.g., by using selective chemical etching or plasma etching.

Advantageously, contamination of the electrode with another metal can beprevented since the electrode material is applied additively to thesubstrate and is not deposited onto the substrate using a (metallic)intermediate carrier. Electrodes comprised of highly pure metals can becreated on dielectric substrates, in particular on polymers. Forexample, it is possible to deposit pure gold on a dielectric, i.e.,non-conductive, organic substrate (e.g., polyimide, LCP, etc.), withoutit becoming contaminated by other metals. Once deposition is complete,only the gold remains, as the electrode, on the surface of thesubstrate. It is therefore possible to create electrodes for componentsthat are designed to be implanted in a human or animal body, and thathave biocompatible properties and that are not expected to interferewith the function or the implantation site due to unwanted metalliccomponents in the electrodes.

There is no risk whatsoever of uncontrolled alloying of the metallicelectrode material with another metal. The metallic electrode materialis applied to the substrate only in an additive manner. Less chemistryand material are therefore required.

According to an advantageous development, current can flow primarilyacross the electrically conductive polymer layer duringelectrodeposition. To perform electrodeposition, the substrate is coatedonly in conductive regions, thereby ensuring that the metallic electrodematerial is deposited only on exposed, i.e., resist-free, regions of theelectrically conductive polymer layer. Electrodeposition basically makesit possible to deposit a metal having very high purity. A highly pureelectrode can be deposited on a dielectric substrate. The electricallyconductive polymer layer makes it possible to avoid using metallic leadson the substrate, thereby eliminating the need to apply foreign metalsin the vicinity of the metallic electrode material to close theelectrical circuit during electrodeposition.

Furthermore, as an alternative, a method for the electrodeposition of anelectrode including a metallic electrode material on a dielectricsubstrate is provided, comprising the following steps:

-   -   Applying a metallic conductive layer onto the substrate;    -   Patterning the metallic conductive layer to create exposed        regions on the substrate;    -   Depositing an electrically conductive polymer layer at least in        the exposed regions;    -   Masking the electrically conductive polymer layer in the exposed        regions and/or mask the remaining metal layer using a mask;    -   Electrodepositing of the metallic electrode material on the        electrically conductive polymer layer;    -   Removing the mask; and    -   Removing or deactivating the excess conductive polymer layer.

When depositing the electrically conductive polymer layer at least inthe exposed regions, then, depending on the process used to deposit theconductive polymer, the deposition can take place selectively on theexposed polymer or on the entire surface, including the metallicelectrode material. Favorable deposition processes are, e.g.,selectively from an aqueous solution only on the polymer using EnthoneEnvision HDI (formerly DMS-E process) from Enthone, Inc., in West Haven,Conn., USA, selectively from an aqueous solution only on the polymerusing Atotech Seleo CP Plus from Atotech Deutschland GmbH in Berlin, ora non-selective deposition from the gas phase using plasma coating.

The excess conductive polymer layer can be deactivated (i.e., minimizethe conductivity), e.g., by reduction or oxidation of the conductivepolymer. As an alternative, the conductive polymer can also be removed,e.g., using selective chemical etching or plasma etching.

Favorable materials for electrically conductive polymers are, e.g.,polyaniline, polypyrrole, polythiophene, and the like.

The polymer layer should be as thin as possible to ensure easy removal,but should be so thick that the electrical conductivity suffices formetal deposition. A reasonable thickness can be, e.g., below 10 μm atthe most. Exact limits can vary depending on the actual system and areidentified easily using tests. A thickness of the noble metal layer isdefined by the necessary stability of the conductor and the currentintensity or resistance that is acceptable for the application. Theadvantage of such a deposition compared to direct noble metal depositionfrom the gas phase is that greater thicknesses of noble metal can bedeposited, which is useful. The maximum thickness of the conductor islimited in practical application only by the thickness of the resist.Favorable conductor thicknesses can be, e.g., in a range of 0.5 μm to100 μm.

Advantageously, according to the alternative variant, contamination ofthe electrode with another metal can be prevented since the electrodematerial is applied additively to the substrate and is not depositedonto the substrate using a (metallic) intermediate carrier. Electrodescomprised of highly pure metals can be created on dielectric substrates,in particular polymers. For example, it is possible to deposit pure goldon a dielectric, i.e., non-conductive, organic substrate (e.g.,polyimide, LCP, etc.), without it becoming contaminated by other metals.Once deposition is complete, only the gold remains, as the electrode, onthe surface of the substrate. It is therefore possible to createelectrodes for components that are designed to be implanted in a humanor animal body, and that have biocompatible properties and that are notexpected to cause interference due to unwanted metallic components inthe electrodes.

There is no risk whatsoever of uncontrolled alloying of the metallicelectrode material with another metal. The metallic electrode materialis applied to the substrate only in an additive manner. Less chemistryand material are therefore required.

According to an advantageous development of the alternative variant,during electrodeposition through a portion of the mask, the metallicconductive layer can be separated from the region in which the metallicelectrode material is to be deposited, wherein the metallic conductivelayer tightly encloses the region. A portion of the current cantherefore flow across the relatively low ohmic metallic conductive layerduring electrodeposition.

According to an advantageous development of the alternative variant,current can flow primarily across the conductive layer duringelectrodeposition. Advantageously, this takes place into the vicinity ofthe electrode to be electrodeposited. The electrically conductivepolymer layer can carry the current flow in the region between theconductive layer and the electrode to be deposited. The metallicconductive layer does not come in contact with the metallic electrodematerial. The metallic conductive layer has lower resistance than doesthe electrically conductive polymer layer, thereby resulting in bettercurrent distribution and therefore better distribution of the layerthickness of the electrode metal.

During electrodeposition, the substrate is coated only in conductiveregions, thereby ensuring that the metallic electrode material isdeposited only on the electrically conductive polymer layer since theconductive layer is advantageously covered with photoresist duringelectrodeposition. The electrically conductive polymer layer that existsin the region in which the metallic electrode material is to bedeposited makes it possible to avoid using metallic leads in thisregion, thereby preventing foreign metals from coming in contact withthe metallic electrode material to close the electrical circuit duringelectrodeposition.

According to an advantageous development of the alternative variant, theconductive layer can be coated with a diffusion barrier layer before theelectrodeposition of the metallic electrode material. This furtherreduces the risk of contamination of the metallic electrode materialwith the material of the metallic conductive layer.

According to an advantageous development of the alternative variants,nickel and/or palladium can be used as the diffusion barrier layer.These materials are characterized, e.g., by an effective inhibition ofdiffusion processes.

Advantageously, a photoresist mask can be used to mask the electricallyconductive polymer layer in both variants of the proposed method. Aphotoresist is easily applied, patterned, and removed. The surface ofthe deposited electrode does not come in contact with the photoresistduring electrodeposition, and does so only briefly in the solvent whenthe photoresist is removed, or practically not at all when a physicaletching method or oxidation method is used.

Advantageously, for both variants of the proposed method, theelectrically conductive polymer layer outside of the deposited metallicelectrode material can be removed, or the electrical conductivity of theelectrically conductive polymer layer outside of the deposited metallicelectrode material can be reduced.

A noble metal or an alloy of noble metals (e.g., platinum/iridium) canbe used as the metallic electrode material for both variants of theproposed method. For example, gold or platinum are advantageously usedas the metallic electrode material. A suitable organic substrate is apolymer that is well suited for use for components having electrodesthat are implantable in the human and/or animal body, in particular PI(PI=polyimide) or LCP (LCP=liquid crystal polymer). The methods can beoperated, in all, at low temperatures, e.g., room temperature, therebyprotecting the organic substrate from the effect of excessivetemperatures.

Various other objects, aspects and advantages of the present inventioncan be obtained from a study of the specification, the drawings, and theappended claims.

DESCRIPTION OF THE DRAWINGS

The invention is explained in the following in greater detail withreference to embodiments that are depicted in drawings. They show, in adiagrammatic representation:

FIGS. 1A-1F show various method steps in the galvanic coating of adielectric substrate with a metallic electrode material;

FIGS. 2A-2H show various method steps in the galvanic coating of adielectric substrate with a metallic electrode material, using ametallic conductive layer; and

FIGS. 3A-3H show various method steps in an alternative galvanic coatingof a dielectric substrate with a metallic electrode material, using ametallic conductive layer that is in contact with a barrier layer atselective points.

Elements that are functionally identical or similar-acting are labeledusing the same reference numerals in the figures. The figures areschematic depictions of the invention. They do not depict specificparameters of the invention. Furthermore, the figures merely showtypical embodiments of the invention and are not intended to limit theinvention to the embodiments shown.

DETAILED DESCRIPTION

FIGS. 1A-1E show sectional views of various method steps to coat adielectric, in particular organic, substrate 10 with a pure metallicelectrode material 40, in particular a noble metal, e.g., gold. Metallicelectrode material 40 can be deposited, e.g., in the form of a trace onsubstrate 10. Suitable layer thicknesses are, e.g., between 1 μm and 20μm, although greater layer thicknesses, e.g., up to 100 μm can be used.A plurality of electrodes comprised of metallic electrode material 40can also be deposited, of course, without departing from the spirit andscope of the present invention.

Dielectric organic substrate 10, which is comprised of a biocompatiblepolymer such as, for example, PI or LCP in particular, is provided (FIG.1A) and an electrically conductive polymer layer 20 is deposited, e.g.,onto the entire surface (FIG. 1B).

Electrically conductive polymer layer 20 is provided with a mask byapplying and patterning a photoresist, wherein regions 30 ofelectrically conductive polymer layer 20 are covered and one region 32of electrically conductive polymer layer 20 is exposed (FIG. 1C).

Metallic electrode material 40 is electrodeposited on exposed region 32of electrically conductive polymer layer 20 which is used as the powersupply (FIG. 1D). Next, the photoresist is removed (FIG. 1E), therebyleaving pure electrode material 40 on substrate 10. In the final step(FIG. 1F), exposed electrically conductive polymer layer 20 aroundmetallic electrode material 40 is removed, e.g., using chemical and/orplasma etching. As an alternative, the electrical conductivity ofexposed electrically conductive polymer layer 20 can be reduced. Thiscan take place, e.g., using chemical oxidation or reduction.

FIGS. 2A-2H are explained with reference to sectional views of variousmethod steps to coat a dielectric substrate 10 with a metallic electrodematerial 40, in particular a noble metal, e.g., gold, using a metallicconductive layer 12 which is comprised, e.g., of copper. Metallicelectrode material 40 can be deposited, e.g., in the form of a trace onsubstrate 10. A plurality of electrodes comprised of metallic electrodematerial 40 can also be deposited, of course, without departing from thespirit and scope of the present invention.

A metallic conductive layer 12 is applied to a dielectric substrate 10,which is comprised of a biocompatible polymer such as PI or LCP or thelike, in particular being laminated thereon or deposited using a coatingtechnique (FIG. 2A). Conductive layer 12 is patterned to create anexposed region 14 on substrate 10 (FIG. 2B). An electrically conductivepolymer layer 20 is deposited in exposed region 14 of substrate 10 (FIG.2C). Deposition onto the conductive layer 20 does not createinterference if, after deposition of metallic electrode material 40,conductive polymer layer 20 is removed everywhere, as shown in FIGS. 2Fand 2G, or if conductive polymer layer 20 does not interfere with theetching step in FIGS. 2G and 2H.

Conductive layer 12 and electrically conductive polymer layer 20disposed in exposed region 14 are masked using a mask comprised of aphotoresist, wherein covered regions 30 of conductive layer 12 and aregion 34 of electrically conductive polymer layer 20 are covered and aregion 32 of electrically conductive polymer layer 20 is exposed (FIG.2D). Conductive layer 12 is moved close to exposed region 32—to becoated—of electrically conductive polymer layer 20, while remainingseparated from exposed region 32 by regions 34 of the photoresist.

Metallic electrode material 40 is electrodeposited onto exposed regions32 of electrically conductive polymer layer 20 (FIG. 2E). Duringelectrodeposition, current flows mainly across (covered) conductivelayer 12 and across electrically conductive polymer layer 20 only in thedirect vicinity of region 32 to be coated. Despite the relativelylow—compared to conductive layer 12—electrical conductivity ofelectrically conductive polymer layer 20, homogeneous electrodepositioncan take place on exposed electrically conductive polymer layer 20. Dueto the coverage by regions 34, the metal of conductive layer 12 does notcome in direct contact with deposited metallic electrode material 40,thereby preventing or at least minimizing inter-diffusion between thetwo metals.

After the photoresist is removed from around the deposited metallicelectrode material 40 (FIG. 2F), the excess exposed electricallyconductive polymer layer 20 is removed, e.g., using chemical etching orplasma etching or chemical oxidation, or at least the electricalconductivity thereof is greatly reduced (FIG. 2G). Conductive layer 12can then be removed selectively, e.g., etched selectively. For thispurpose, a photoresist having a negative mask of the pattern of thephotoresist in FIG. 2D can be applied.

A portion of conductive layer 12 can remain where only electricalcurrents are transported on the same plane of substrate 10 (FIG. 2H),thereby rendering a function as an electrode unnecessary. It istherefore possible to minimize the quantity of metallic electrodematerial 40 that is deposited. If electrical contacting is requiredbetween remaining conductive layer 12 and the electrode comprised ofmetallic electrode material 40, conductive layer 12 can be coatedlocally in the contact region with a diffusion barrier layer, e.g.,comprised of nickel or palladium.

Metallic electrode material 40 can be electrically connected to metallicconductive layer 12 using the process chain described in FIGS. 3A-3H.Diffusion into the electrode, which is composed of metallic electrodematerial 40, is prevented or at least reduced by applying a diffusionbarrier layer 16 in the connection region. If the connection region isseparated from the electrode region by a considerable distance, e.g., afew millimeters, then any residual diffusion that occurs is negligible.If diffusion barrier 16 is a metal that can be etched at the same timeas metallic conductive layer 12 (e.g., Cu and Ni), then diffusionbarrier 16 can be applied to the entire surface.

A metallic conductive layer 12 is applied to a dielectric substrate 10,which is comprised of a biocompatible polymer such as PI or LCP or thelike in particular, i.e., being laminated thereon or deposited using adeposition technique (FIG. 3A). Conductive layer 12 is patterned onsubstrate 10 to create an exposed region 14, and a diffusion barrierlayer 16, which is comprised, e.g., of nickel or palladium, is depositedonto conductive layer 12 (FIG. 3B). This variant is favorable if the aimis to electrically connect metallic electrode material 40 to metallicconductive layer 12. An electrically conductive polymer layer 20 isdeposited in exposed region 14 of substrate 10 (FIG. 3C). Depositiononto metallic conductive layer 12 does not create interference if, afterdeposition of metallic electrode material 40, conductive polymer layer20 is removed everywhere, as shown in FIGS. 3F and 3G, or if conductivepolymer layer 20 does not interfere with the etching step in FIGS. 3Gand 3H.

Conductive layer 12 and electrically conductive polymer layer 20disposed in exposed region 14 are masked using a mask comprised of aphotoresist, wherein covered regions 30 of conductive layer 12 and aregion 34 of electrically conductive polymer layer 20 are covered, and aregion 32 of electrically conductive polymer layer 20, and a region 35of the conductive layer are exposed (FIG. 3D). Since perfectregistration is not possible, a small region above the conductive layermust also be exposed.

Metallic electrode material 40 is electrodeposited onto exposed regions34 of electrically conductive polymer layer 20 (FIG. 3E) and region 35on the exposed conductive layer. During electrodeposition, current flowsmainly across (covered) conductive layer 12 and across electricallyconductive polymer layer 20 only in the direct vicinity of region 32 tobe coated. Despite the relatively low—compared to conductive layer12—electrical conductivity of electrically conductive polymer layer 20,homogeneous electrodeposition can take place on exposed electricallyconductive polymer layer 20. The electrodeposited electrode metal is incontact with the conductive metal only in selective region 35. Thediffusion of the conductive metal into the electrode metal is minimizedthere by a diffusion barrier of the electrode material. Since contactbetween the two metals is only very local, the contact region can beselected in a manner such that it is separated from the active electrodesurface by a very large distance, thereby making it possible to furtherminimize the risk of diffusion.

After the photoresist is removed from around the deposited metallicelectrode material 40 (FIG. 3F), the excess exposed electricallyconductive polymer layer 20 is removed, e.g., using chemical etching orplasma etching, or at the least the electrical conductivity thereof isgreatly reduced (FIG. 3G). Conductive layer 12 and diffusion layer 16can then be removed selectively, e.g., etched selectively. For thispurpose, a photoresist having a negative mask of the pattern of thephotoresist in FIG. 3D can be applied.

A portion of conductive layer 12 can remain where only electricalcurrents are transported on the same plane of substrate 10 and afunction as an electrode is therefore unnecessary (FIG. 3H). It istherefore possible to minimize the quantity of metallic electrodematerial 40 that is deposited. If electrical contacting is requiredbetween remaining conductive layer 12 and the electrode comprised ofmetallic electrode material 40, diffusion barrier layer 16 protectsconductive layer 12 locally in contact region 16 a. This region issituated far enough away from the actual electrode region. If, e.g.,nickel is used as diffusion barrier layer 16, then nickel can be etchedusing copper and does not interfere with this final etching step. If thediffusion layer interferes with the subsequent processes, they can beremoved by selectively etching the conductive layer. The diffusion layerremains intact in the interface region (16 a).

This embodiment is favorable when the aim is to use substrate 10, whichhas been coated in this manner, as a biocompatible electrode and as acarrier for components or as a cable outside of the body. A costadvantage is obtained if noble metal is used only to form the criticalregions. The non-critical regions can be made of metallic conductivelayer 12 which is already disposed on substrate 10.

The invention results in a patterned galvanic structure of metalconductors (e.g., Au) on a dielectric base material (substrate 10) usinga conductive polymer. The metallic electrode material is applied only inan additive manner, thereby minimizing the chemistry and materialsrequired.

It will be apparent to those skilled in the art that numerousmodifications and variations of the described examples and embodimentsare possible in light of the above teachings of the disclosure. Thedisclosed examples and embodiments are presented for purposes ofillustration only. Other alternate embodiments may include some or allof the features disclosed herein. Therefore, it is the intent to coverall such modifications and alternate embodiments as may come within thetrue scope of this invention, which is to be given the full breadththereof. Additionally, the disclosure of a range of values is adisclosure of every numerical value within that range.

1-2. (canceled)
 3. A method for the electrodeposition of an electrodeincluding a metallic electrode material on a dielectric substrate,comprising the following steps: applying a conductive layer onto thesubstrate; patterning the conductive layer to create exposed regions onthe substrate; depositing an electrically conductive polymer layer atleast in the exposed regions; masking the conductive layer and theelectrically conductive polymer layer in the exposed regions and/ormasking the remaining metal layer using a mask; electrodepositing themetallic electrode material on the electrically conductive polymerlayer; removing the mask; and removing or deactivating the excessconductive polymer layer.
 4. The method according to claim 3, wherein,during electrodeposition through a portion of the mask, the conductivelayer is separated from the region provided for deposition of themetallic electrode material, wherein the conductive layer tightlyencloses the region.
 5. The method according to claim 3, wherein currentcan flow primarily across the conductive layer during electrodeposition.6. The method according to claim 3, wherein the conductive layer iscoated with a diffusion barrier layer before the electrodeposition ofthe metallic electrode material.
 7. The method according to claim 3,wherein the conductive layer is removed at least in regions. 8-11.(canceled)
 12. A method for the electrodeposition of an electrodeincluding a metallic electrode material on a dielectric substrate,comprising the following steps: depositing a metallic conductive layeron the substrate; patterning the metallic conductive layer so that atleast one region of the substrate remains exposed; depositing adiffusion barrier layer on the metallic conductive layer; depositing anelectrically conductive polymer layer in the at least one exposedregion; masking the metallic conductive layer and the electricallyconductive polymer layer in the at least one exposed region using amask; electrodepositing the metallic electrode material on exposedregions of the electrically conductive polymer layer and the metallicconductive layer; removing the mask; and removing the excess conductivepolymer layer or deactivating the excess conductive polymer layer byreducing the electrical conductivity of the electrically conductivepolymer layer outside of the deposited metallic electrode material. 13.The method according to claim 12, wherein current can flow primarilyacross the electrically conductive polymer layer duringelectrodeposition.
 14. The method according to claim 12, wherein aphotoresist mask is used to mask the electrically conductive polymerlayer.
 15. The method according to claim 12, wherein the electricallyconductive polymer layer is removed outside of the deposited metallicelectrode material.
 16. The method according to claim 12, wherein theelectrically conductive polymer layer is at most 10 micrometers thick.17. The method according to claim 12, wherein a noble metal or an alloyof noble metals is used as the metallic electrode material.
 18. Themethod according to claim 12, further comprising selectively etching themetallic conductive layer and the diffusion barrier layer.